A machine’s undercarriage needs special attention as it supports the entire machine weight and performs in tough terrains, over obstacles and abrasive materials like silica, sand etc, says Bhaskarudu Peddakotla.
The durability and life of the machine’s undercarriage impacts the operating cost of the machine and has a significant effect on the overall production cost and productivity of the machine. The expenses on account of the undercarriage are next to that of the fuel used in bulldozers and excavators and track type loaders. In fact, the operation cost incurred on account of the undercarriage is affected by the machine’s configuration, its operation and maintenance. So, the undercarriage cannot be ignored as it supports the machine’s entire weight and must perform efficiently in the roughest of terrains and counter abrasive materials like silica and sand, which is more abrasive than rock.
Machine configuration during purchase: Equipment manufacturers offer their machines with various types of undercarriages specific to the machine’s applications. Hence, the indenter should consider factors like material hardness, fragmentation, operating conditions, and productivity during the machine’s configuration. The choice of undercarriage should also be based on the materials handled by the machine. These have been categorized under four broad categories:
- High impact and High abrasive
- High impact and Low abrasive
- Low impact and High abrasive
- Low impact and Low abrasive
Operator skills: A skilled operator will keep a constant watch on the machine and listen to any sounds made by it. The present generation machines have sophisticated electronics and hydraulics, and a comfortable operator cabin. While these are intended to reduce operator fatigue and improve productivity, the operator must continue to observe and sense the stress being put on the machine parts that are bearing the entire load of the machine running on tough underfoot conditions. The operators must be trained to inspect any abnormal sound during operation, and undertake daily physical inspection of all visible parts such as track shoes, links, bushings, idlers, bottom rollers, top rollers, roller guards, sprockets and fasteners for any crack, bend, looseness, wear and tear, etc.
Maintaining correct sag of track chains: Certain amount of sag as recommended by the machine manufacturer has to be maintained in track chains to minimise friction. Too much tension in track chain leads to spalling, faster wear of all mating components, and even higher fuel consumption because of excess load. Sometimes, a track chain with a recommended sag may get tension due to packing of material; hence, it is advised to adjust the track tension based on the working condition.
Too loose a track chain can cause derailing, or the chain may pop out from the sprocket. There may be unusual impacts between parts with possible chipping and spalling. Natural wearing of links, rollers, idlers, sprockets etc. over a period of time causes loosening of the track. So, this must be observed and measured as per the defined procedure and adjusted to the recommended limit. Track tension or sag adjustment is a simple process in any machine; it can be done by pumping or releasing grease from a cylinder provided for the job. Ensure that there are no leaks in the grease seals. The machine’s inspection must include checking the sag at defined intervals.
Cleaning: Mud accumulation or packing of soil/sand in between moving parts is a common phenomenon in machines. The packing of sand or soil not only increases the track tension but also acts as a grinding media between the parts and causes rapid wear and tear. It also puts an extra load on the powertrain of the machine, which leads to excess fuel consumption and shortens the life of the clutch packs. So, regular cleaning of the machine is necessary to minimize wear and tear of the undercarriage parts.
Speed: Operating the machine at high speeds accelerates the wear and tear rate of the undercarriage components. It is a tendency of the operators of dozers and track loaders to reverse the machines at a very fast speed. This is because during forward travel, they have to push the material with a full width of blade (in case of a dozer) or the bucket of material to be loaded (in case of a track type loader). Hence, due to the natural resistance of the material, the machine cannot move forward with great speed.
Due to the design configuration of the undercarriage (idlers are in the front, sprockets are in the rear, and the track sag is on top), the contact area between bushing and sprocket teeth will be more during reversing (about 75%) as compared to forward travel (about 25%). Greater the contact area, more the friction and ultimately more wear and tear of the parts. Operators also tend to run the machine at a high speed when moving from one location to another. Hence, they must be educated on the impact of speed on the life of the undercarriage.
Negotiating curves: Sharp turns and counter rotations increase contact stresses between components, causing damage and faster wear of components. Operators need to slow down the machine when negotiating turns.
Machine orientation: This applies particularly in sidehill operation during which the machine will have more load between the link side-face and roller flange, which causes accelerated wear of both link and roller. This type of wear and tear reduces the link width (unlike rail wear during operation in flat ground) which leads to further link wear. The operator should therefore keep changing the position of the machine by turning it on both sides.
Avoid unwanted travel: It is advisable to have a mobile maintenance facility for oil filter change, fuelling, washing etc., nearer to the machine, rather than taking the machine to a garage. This way, a lot of travelling can be avoided, and the wear and tear reduced. Operators tend to run an empty machine at a high speed.
Maintenance: Preventive maintenance through condition monitoring is critical for extending the life of the undercarriage. The maintenance team must keep a checklist of all components of the undercarriage. Based on operating conditions, regular inspection intervals should be decided in consultation with the machine manufacturer’s service representative. The machine should be cleaned thoroughly before inspection and proper tools are to be used for taking the measurements.
No approximations should be entered in the check sheet. Once the inspection is completed, the data must be analysed on the wear and tear of each and every component and an assessment made on the expected residual life. This not only helps in meticulous planning of parts and servicing but also minimizes machine downtime. Sometimes, an inspection may reveal that the sprocket needs to be changed twice for every change of track link assembly. A systematic approach will help in maximizing component life and minimizing downtime of the machine.
In addition, the maintenance team must also analyse the operational data obtained from the machine reports such as travel percentage of the machine, speed of travelling etc., based on which the team can prepare an action plan to bridge the gaps and accordingly advise the operator.